Waste natural gas-based atmospheric water harvesting

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Abstract

Excess natural gas produced in oilfields and emitted from landfills is predominantly flared or vented. These practices are responsible for large scale energy waste, greenhouse gas emissions and a host of other environmental issues such as light, noise and smoke pollution. Globally, 4% of gas production at oilfields is flared; locally the percentages can be significantly higher. Methane equivalent to 14% of US residential natural gas consumption is emitted from US landfills.
This dissertation analyzes a new technology, wherein excess gas powers a refrigeration cycle to condense atmospheric moisture from air. Waste gas-based atmospheric water harvesting (AWH) from oilfields and landfills can enable new options to monetize waste gas, and also address water issues associated with oilfield operations. In-depth modeling is conducted to estimate the water harvest, which depends on the volume of waste gas, ambient weather, and the refrigeration system utilized.
The benefits of oilfield gas-based AWH are quantified for the Eagle Ford (Texas) and Bakken (North Dakota) Shales, the two largest flaring hotspots in the US. Overall, oilfield gas-based AWH can meet 36% and over 100% of annual water requirements of the Eagle Ford and Bakken Shales, respectively. The benefits of landfill gas(LFG)-based AWH are quantified for the Barnett Shale (Texas) and Kern County (California), which can be served by 30 landfills each. The water harvested from LFG-based AWH can meet 34% and 12-26% of water requirements in the Barnett Shale and Kern County oilfields, respectively. A techno-economic analysis is also carried out to quantify the economic feasibility of large scale LFG-based AWH projects. Overall, waste natural gas-based AWH can offer signiﬁcant economic beneﬁts while addressing key environmental issues.
This dissertation also briefly discusses two alternative uses of landfill gas. These are the use of LFG for ammonia production (which is the starting point for fertilizers), and the use of LFG for electricity generation (by routing LFG to nearby power plants). Analysis of LFG emissions in Texas indicates that LFG can be used to produce 3,200 tons of ammonia daily, for agricultural use. In Texas, routing the LFG to nearby gas-fired power plants will increase statewide installed capacity by 3%. In particular, five power plants in Texas can increase their capacity by more than 10%.
Overall, this dissertation outlines many novel waste-to-value conversion technologies which address energy waste and environmental issues, while benefiting the water, food and electricity sectors. The technologies discussed in this dissertation have global applicability, which should be explored in follow up studies.